Body Mass Index (BMI)

Body Mass Index (BMI) is a numerical measure of body size calculated as an individual’s weight in kilograms divided by the square of their height in meters (kg/m²). It is widely used as a screening tool to categorize adults into standard weight status classifications defined by the World Health Organization: underweight (<18.5 kg/m²), normal weight (18.5–24.9 kg/m²), overweight (25.0–29.9 kg/m²), and obesity (≥30.0 kg/m²); in children and adolescents, BMI is interpreted using age- and sex-specific percentile curves.

While BMI is inexpensive, non-invasive, and useful for population-level surveillance, it has well-recognized limitations — it does not distinguish between fat and lean mass, does not account for fat distribution, and its accuracy varies by age, sex, ethnicity, and body composition — and is therefore increasingly used alongside additional measures such as waist circumference, body composition analysis, and metabolic markers.